The coating of an optical fiber having a core and a cladding includes two layers of a primary coating layer and a secondary coating layer in consideration of obtaining mechanical strength and suppressing microbend loss (for example, see Patent Literature 1). Non-Patent Literature 1 discloses that the microbending resistance of an optical fiber is related to the lateral rigidity D and flexural rigidity H of the optical fiber and can be obtained by the following formulas. In addition, in Patent Literature 2, there is description of microbend loss considered based on Non-Patent Literature 1.
                              [                      Formulas            ⁢                                                  ⁢            1                    ]                ⁢                                                                                                a          micro                ∝                  D                      H            2                                              Formula        ⁢                                  ⁢                  (          1          )                                        H        =                                            H              g                        +                          H              s                                =                                                                      π                  ⁢                  r                                g                4                            ⁢                              E                g                                      +                                          π                ⁡                                  (                                                            r                      s                      4                                        -                                          r                      p                      4                                                        )                                            ⁢                              E                s                                                                        Formula        ⁢                                  ⁢                  (          2          )                                        D        =                              E            p                    +                                    (                                                E                  s                                -                                  E                  p                                            )                        ⁢                                          (                                                      E                    p                                                        E                    s                                                  )                                            2                /                3                                      ⁢                                          (                                  2                  ⁢                                                                                    r                        s                                            -                                              r                        p                                                                                                            r                        s                                            -                                              r                        g                                                                                            )                                            3                /                2                                                                        Formula        ⁢                                  ⁢                  (          3          )                    